The termination of flat cables has, in the past, been accomplished in the main through the techniques of soldering, crimping and insulation displacement. Soldering is both expensive and, with a fine cable pitch, is subject to bridging, shorting, or delamination. Crimping has not been practical on a pitch less than 0.05 inches. This is a result of the footprint size of a crimped joint in which adequate metal cold flow occupies significant real estate. For gas-tight insulation displacement connection in which pointed, jawed contacts pierce a thin flat cable from a direction orthogonal to the flat top or bottom surface of the cable, the problem is that the cable is only contactable from one side. One such insulation displacing connector is the telephone modular jack connector commonly employed for three and four pair telephone cables. Note when the term "pitch" is used herein, pitch is defined as the center-to-center spacing of the ends of the conductors in the cable.
More recently, single-sided flat cables have been manufactured with conductors having a pitch of less than 0.050 inches and cable connection systems for such cables involve soldering, crimping and the use of the common telephone modular plugs. For the purposes of this patent, a cable having a conductor pitch of less than 0.05 inches is considered to be a narrow-pitch cable. Note, for narrow-pitch cables the connection systems to date have been single-sided. Telephone cable requirements now envision a two-sided cable having a pitch of 0.0425 inches which involves too small a space to be accommodated by standard single-sided flat cable connectors. As the number of conductors per inch increases, with concomitant decrease in pitch, there is a need for a connector which can accommodate such small pitches without the necessity of converting the position of the conductors to a more spread out or fanned out pattern in order to effectuate proper connection.
Thus, while it is indeed possible to make some sort of connection to flat cables of such small pitch, the connectors associated with the small-pitch cables in general either are single-sided or rely on internal electrical paths within the connector body which fan out or spread out the conductor paths, such that oversized mating male or female conductors must be utilized. With a drive to miniaturization, especially in providing narrow cables, it is desirable to provide a connector which has a connector body having connector contact paths or channels which do not utilize the fan out approach in order to provide for appropriate connection.
Likewise, when such cables are to be connected to printed circuit boards it is desirable to minimize the amount of circuit board real estate utilized when mounting contacts to the printed circuit board. The limiting factor is primarily the hole spacing between the holes utilized to accommodate the leads of the contacts which pass through the holes and are soldered to the printed circuit board by conventional wave soldering or other techniques. The limit to the lateral spacing of the holes relates to the amount of dielectric material between the hole pads to insure against sorting or other failures. In general, for pitches of 0.0425 inches, the lateral spacing of printed circuit board holes leaves too little dielectric material between the holes when the holes are patterned in a straight line.
A further problem with ultra-thin flat cables which may be on the order of 0.024 inch thickness is that connectors which attempt to resiliently contact such cables have insufficient resilience due to the thinness of the cable. For instance, wireform contact clips such as commercially available from Digiclip Corporation of Denville, N.J. are in general utilized for connecting one circuit board to another. The gaps in the openings of these clips are generally on the order of 0.058 inches, which accommodates the typical thickness of a printed circuit board. However, when attempting to utilize commercially available clips with respect to ultra-thin cables, the spring properties of such wires are insufficient when the gaps in the clips are brought down to the 0.024 inch spacing required for the ultra-thin cables. Thus, it is impossible to utilize such clips to connect directly to the ultra-thin flat cables. Note, for purposes of this patent, "ultra-thin" refers to flat cables having a thickness less than 0.030 inches.
As mentioned before, one of the further drawbacks with respect to the aforementioned telephone type modular male connectors is that they are only capable of connecting to conductors from one side of the cable. It is only with difficulty that these connectors can be utilized for those cables in which is it desirable to contact some of the conductors from one side of the cable, while contacting other of the conductors from the other side of the cable. Such cables in which connection to conductors is to be made from alternating sides of the cable are those cables in which some sort of shield is placed or embedded between adjacent conductors or conductor pairs within the cable. Should a cable have a shield placed to one side of a conductor, then contact to this conductor must be made from the side of the cable away from the shield. Should a conductor be placed on the other side of the embedded shield, then connection to this conductor must be made from an opposite side of the cable, a situation which is accommodated only with great difficulty in terms of the aforementioned modular male connector.
A further problem associated with the utilization of ultra-thin cables is that the amount of dielectric insulation associated with these cables is exceedingly small. Thus, contacts which in any way cut through or displace such insulation are confronted with dielectric isolation problems in which electrical breakdown can easily occur in such fragile structures. Thus, any connector which can add dielectric thickness to the relatively thin cable, increases the dielectric strength of the cable-connector combination which is of obvious desirability.
In summary, for thin narrow-pitch flat cables there is a requirement for double sided connection to the cable in which real estate on the associated printed circuit board is to be minimized and in which the size of the ultimate connector is also to be minimized. Thus, the aforementioned fanned or expanding conductor structure within a connector body is to be avoided. The production of such a connection system which can maintain the relatively small pitch of the cable should also desirably include means for increasing the dielectric strength of the connector, thereby to prevent dielectric breakdown when the thin fragile cables are terminated and connected to printed circuit boards. Finally, there must be some accommodation to the relatively thin nature of the cable to permit ohmic contact to be made by relatively large-apertured spring-loaded contacts. All of the above must be accomplished without substantially altering the relatively narrow pitch established by the cable, such that real estate on the printed circuit board or other substrate is minimized in the lateral direction, and such that the original pitch established by the cable is not enlarged by the connection to the printed circuit board or substrate.